@mcavoym1 As far as I know, QuickBooks has no way to do that. Would be handy, though.
When I run across this issue, I typically set up an Excel sheet with a couple formulae. This allows the person handling payroll to enter the Net Pay into a cell and see how much they should be holding out for child support.
I prefer using the IF formula for this, but I imagine there are a lot of ways to set up the required formulae in Excel.
